Optical vortices crystals: Spontaneous generation in nonlinear semiconductor microcavities

Broad-area, vertical-cavity surface-emitting lasers were shown to switch th eir emission mode from the regular single or multilobed Light fields to exh ibit complex arrays of "dark beams." Examination of these dark spot arrays revealed that they consist of multiple, closely packed optical vortices: op tical fields that have phase singularities and show increased complexity as the injection current Level is raised. Contrary to their complex appearanc e, most of these Light distributions are not the result of a multimode (mul tiple-frequency) operation but exhibit single-frequency characteristics. Th e dark beam patterns can be described as emanating from a spontaneous proce ss of transverse mode Locking of nearly degenerate modes, assisted by the L aser nonlinearity. Surprisingly, these patterns show high resemblance to pa tterns generated in other nonlinear scenarios that are completely different both in scale and in mechanism.